Piston



United States Patent Ofilice 3,319,575 Patented May 16, 1967 This invention relates generally to fluid pressure translating devices of the reciprocating type, and more particularly to a new and improved piston construction adapted for use in hydraulic pumps or motors.

In the axial, as well as radial, piston types of pumps and motors, as the operating speed of the unit increases, the inertia forces on the piston increase in proportion to the square of the speed. Thus, in a high speed and high pressure hydraulic pump or motor the pistons and cylinders are subjected to high stresses and high rubbing velocities. In order to reduce the effects of these high inertia forces, it is desirable that the piston be made of a Wearresistant material capable of withstanding high stresses, While at the same time it is necessary that the piston be made as light as possible. In order to reduce the weight of the piston, it is conventional to remove the center section of the piston .by means of a drilled or otherwise formed cavity.

In the use of prior hollow piston constructions, it has been found that adverse side effects are introduced into the system due mainly to the compressibility of the oil which fills the hollow piston cavity. The compressibility of the fluid has a marked effect upon the over-all efliciency of the unit and also produces cavitation, erosion, noise and undesirable fluid pressure moments on the swashplate mechanism when used in an axial piston type pump or motor.

The general purpose of the present invention is, therefore, to provide a light Weight piston device of the type having an axially extending lubrication passage therein or use in a hydraulic pump or motor which obviates the disadvantages noted above. To achieve this, the present invention generally consists of a piston having an elongated integral piston body with a spherical slipper projection at one end and a generally flat surface at the other end defining the working face of the piston with an axially extending lubrication passage through the integral body, an annular recess in the body between the working end and the spherical projection, and a cylindrical cover member enclosing the recess.

Another prior type of lightweight piston has a hollow interior filled with a lighter material than the piston casing, but these have the problem of retaining the plugs in position during extended hard use.

A primary object of the present invention is to provide a new and improved piston construction of the character :lescribed above including an inseparable piston assembly :hat is virtually free from mechanical failure, resists cavi- :ation and erosion, and has no critical temperature limitaion.

Another object of the present invention is to provide a lew and improved piston construction for a hydraulic )ump or motor including an elongated recessed integral riston body having a generally spherical projection at one nd adapted to be received by one of the swashplate slipers of the hydraulic pump or motor, with the other end of he integral body defining a portion of the Working face of 1e piston with a lubrication passage extending axially lrough the body so that the slippers may be adequately lbrica-ted by working fluid; the piston body further having [1 annular recess extending radially therein to reduce the 'eight of the over-all piston with the recess having a diamfer substantially less than the diameter of the over-all pis- )11, and a separate cylindrical sleeve-like cover extending over a major portion of the length of the piston body and completely enclosing the recess.

A further object of the working fluid will be transferred through the integral body member to the swashplate of the hydraulic unit.

A still further object of the present invention is to provide a new and improved piston construction of the character described including an annular recess extending axially from the Working face of the integral body member with an annular plug fixed in the recess adjacent the working face of the piston.

Another object of the present invention is to provide a new and improved multiple piston hydraulic unit of the type employing a rotating cylinder block with pistons slidable therein having spherical projections engaged and driven through slippers by a relatively stationary cam member with the improved piston constructions of the character and detail described above.

These and other objects of the present invention will become readily apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a hydraulic pump or motor employing lightweight pistons according to the present invention;

FIG. 2 is a longitudinal sectional view of a piston incorpocriating the first embodiment of the present invention; an

FIG. 3 is a longitudinal sectional view of a piston incorporating a second embodiment of the present invention.

While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will herein be described in detail several embodiments of the invention and modifications thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. The scope of the invention will be pointed out in the appended claims.

Referring now to the drawings, and more particularly FIG. 1, an axial piston pump is generally designated by the numeral 10. It should be understood that the pump 10 could equally well be employed as a motor rather than a pump. The pump 10 includes a generally cylindrical housing member 11 which has a centrally disposed bore 12 for receiving and mounting the outer race of a roller bearing 13. An input shaft 15 is provided for the pump 10 and is rotatably mounted at one end in the inner race of bearing 13. Input shaft 15 may be driven from a suitable prime mover through a coupling 17 splined at both ends thereof, one end of which engages mating female splines in the right end of the input shaft 15 as indicated at 18.

A generally annular end cap 24) closes the right end of bore 12 in the housing 11 and carries a suitable shaft seal 21 to prevent leakage. The other end of the housing member 11 is closed by a generally cylindrical valve plate 27 fixed to the housing member by suitable fasteners (not shown). The valve plate 27 has conventional arcuate inlet and outlet ports formed therein opening to valve face plate 28. The arcuate ports communicate respectively with passages 29 and 30. The passage 29 communicates with a threaded inlet boss 32 (or outlet, depending on the direction of shaft rotation) adapted to re- A centrally disposed bore 36 extending from the valve plate face 28 in the valve member 27 receives a suitable roller bearing 37 of the input shaft 15.

The input shaft 15 has a splined portion 40 which engages mating female splines on a rotatable cylinder block 41. The cylinder block 41 is generally cylindrical in shape and has a porting face 42 which slidably engages the valve plate face 28 when the cylinder block is driven in rotation by the input shaft 15. Suitable springs (not shown) may be provided for urging the cylinder block 41 leftward into engagement with the valve plate face 28 to prevent excessive fluid leakage.

The cylinder block 41 has a pluarlity of axially disposed cylinders 45 in annular array about the axis of rotation of shaft 15. Each of the cylinders 45 communicates with a corresponding arcuate cylinder passage 46 which opens to the port face 42. As the cylinder block rotates the passages 46 serially communicate with the inlet passage 29 and the outlet passage 30. Bonded within each cylinder 45 is a cylindrical sleeve bushing 47 constructed of a suitable bearing metal to reduce the sliding friction and take wear. Pistons 49, described in more detail below, are slidably mounted in the bushings 47. Each piston 49 has a semi-spherical projection 50 at the free end thereof which is received by a semi-spherical socket in one of a plurality of bearing slippers 51.

A fixed cam member 53 mounted within the housing member 11 has a flat camming surface 54 engaging the bearing surface 56 of each of the slippers 51 to reciprocate the pistons 49 in the cylinders 45 as the cylinder block and pistons rotate. It should be understood, however, that while the cam member 53 is shown as being of the fixed displacement type, a variable angle cam member could equally well be employed in the pump 10, as will be apparent to those skilled in this art.

When the hydraulic unit is employed as a pump, a prime mover rotates the cylinder block 41 through the shaft 15, and the pistons 49 are reciprocated in the cylinders by the cam member 53. As the cylinder block rotates, the pistons 49 deliver high pressure fluid through outlet passage 30 as they pass over the outlet port in valve plate 27, and receive inlet fluid through inlet passage 29 as the pistons pass over the inlet port in valve plate 27. A lubricaation passage 57 is provided in each of the pistons for conveying lubricating fluid to the associated slipper member 51. The slippers 51 each have a lubricating pocket 60 opening adjacent the spherical projection 50 on the piston, and a lubricating pocket 61 in the rear surface 56 which communicates through a small passage 63 with the lubricating pocket 60. As the pistons reciprocate, a small quantity of hydraulic fluid in each cylinder 45 passes through passage 57 into the lubricating pocket 63 to provide a lubricating film between the spherical projection 50 and the socket in the slipper 51. Further, fluid in the pocket 60 flows through passage 63 to the lubricating pocket 61 to lubricate the bearing surface 56 on the slipper and the camming surface 54 on the cam member.

Referring now to FIG. 2, wherein the piston 49 is shown in greater detail, the piston is seen to consist generally of an integral elongated body member 70 surrounded by a cylindrical cover member 71. The integral body 70 is generally cylindrical and has a flat radial surface 73 at one end thereof which constitutes a major portion (for example, two-thirds to three-fourths) of the working face of the piston 49. At the other end of the integral body 70 the spherical projection 50 is formed. Much of the force of the fluid in the cylinders 45 is transferred through which rotatably supports the left end the integral body 70 to the cam member 53. This is a distinct advantage over prior pistons that are constructed in multiple parts, as in the present construction mechanical failure due to the loosening of the piston parts is significantly reduced.

The lubrication passage 57 is centrally disposed in the generally cylindrical body 70 and opens at one end to the radial surface 73 and at the other end to the spherical surface of the projection 50. The passage 57 is chamfered as at 74 adjacent the surface 73 and has a reduced portion 75 adjacent the other end of the body member 70, both of which are flow of fluid to the associated slipper. A recess 77 is machined or otherwise formed in the outer cylindrical surface of the integral body member 70 and extends from a plane 78 adjacent but spaced from the working surface 73 axially to a plane 79 adjacent the spherical projection 50. Elimination of this material from the body member 70 significantly reduces the weight of the piston 49 over conventional constructions. The diameter of the cylindrical recessed portion 81 of the body member 70 is sufliciently great so that it will withstand the forces of the working fluid under operating conditions. The recess 77 is preferably formed as at 77a with rounded corner sur-- faces to avoid sharp corners in areas of high stress. The outer cylindrical surface of the body member 70 and the recess 77 define cylindrical mounting surfaces 83 and 84 on the integral body 70. Integral body 70 may, as an example, be constructed of a suitable tool steel such as AISI E52100, but it should be understood that other suitable steels may be employed as well.

The cylindrical tube-like cover member 71 is constructed of the same steel as the body member 70 to eliminate the adverse effects of differential expansion at high temperature operating conditions. Member 71 is sized so that it snugly fits over the cylindrical mounting surfaces 83 and 84 enclosing the recess 77. The cover member 71 is welded as by electron beam welding along the circular parting line 85 and along the circular parting line 86 adjacent the ends of the mounting surfaces 83 and 84, respectively. By known and reliable inspection techniques, strong weld joints may be assured. Subsequent to welding the cover 71 to the body member 70, the piston 49 may be heat-treated to approximately 55 to 60 Rockwell C.

As the cover member 71 and the integral body 70 of the piston 49 are constructed of the same material, the temperature limitation of the piston is much higher than would be expected from a piston fabricated from dissimilar metals.

It should be noted that radial surface 88 on the left end of the cylindrical cover member 71 defines a portion of the working face of the piston 49. This is only a small portion (on the order of one-third) of the total working face. defined also by the radial surface 73 on the integral body 70, so that the cover member 71 absorbs a minor portion of the fluid pressure force. In this manner, the piston 49 acts substantially like a solid piston rather than a multiple part piston and is virtually free from failure due to loosening of the parts.

Referring now to FIG. 3, wherein another embodiment of the present invention is shown, a piston generally designated by the numeral 90 is shown and it may be equally well employed in the hydraulic unit 10 in place of the pistons 49. The piston 90 is generally cylindrical in shape and may be constructed of the same steel as the piston 49, described above. Piston 90 consists generally of an integral body member 91 and an annular plug 92 fixed in the body member 91 adjacent the working face 93. The integral body member 91 has a spherical projection 94 at the right end thereof identical in configuration to the projection 50. A centrally disposed axially extending lubrication passage 95 is formed in the body member 91 by a suitable drilling operation.

The passage 95 has a restricted portion 96 to control adapted to control and improve the the flow of lubricating fluid from the cylinders to the slippers 51. An annular axially extending recess 98 is formed in the body member 91 and extends from the working end thereof to a plane adjacent the projection 94. The recess 98 defines an inner cylindrical wall 97a and a concentric outer cylindrical wall or cover 97b in the integral body member 91. The recess 98 defines two annular working surfaces 99 and 100 which constitute a major portion of the piston Working face 93. The annular plug 92 is fixed in the working end of the piston 90 and has its left surface 101 in the same radial plane with the surfaces 99 and 100 on the integral body 91. The surface 101 thus defines a portion of the working face 93, but similar to the surface 88 on the piston 49 of FIG. 2, constitutes a minor portion of the working face. The plug 92 is fixed to the body 91 as by electron welding the plug along the circular parting lines 103 and 104, respectively.

The advantages obtained with the embodiment of FIG. 3 are substantially the same as those described above with respect to the piston 49.

I claim:

1. A multiple piston hydraulic translating device, comprising: a cylinder block having a plurality of cylinders therein, valve means having inlet and outlet ports, each of said cylinders communicable serially with said inlet and outlet ports as said cylinder block rotates with respect to said valve means, pistons slidable in each of said cylinders including, an elongated rigid cylindrical piston element constructed in one piece and having at one end thereof a generally spherical projection, bearing means engaging said spherical projection, the other end of said element defining a Working face of the piston, said cylindrical element serving to transfer the hydraulic force on said working face to said bearing means, an axial lubrication passage in said element extending from the working face through said spherical projection, an annular recess in the cylindrical surface of said one piece element extending axially from a plane adjacent the projection to a plane adjacent but spaced from said working face, said recess having an inner diameter substantially less than the diameter of the piston, said recess defining spaced cylindrical surfaces on said element one adjacent each end thereof, a separate cylindrical cover surrounding and enclosing said recess being thin with respect to said piston element, the ends of the cover engaging and fixed to the cylindrical surfaces on the one piece element, the outer diameter of the cover being equal to the desired piston diameter, at least one of said surfaces having a diameter throughout its length less than the inner diameter of the cover to permit insertion of the element in the cover, and a cam member for reciprocating said pistons and having a cam surface engaging said bearing means.

2. A multiple piston hydraulic translating device, comprising: a cylinder block having a plurality of cylinders therein, valve means having inlet and outlet ports, each of said cylinders communicable serially with said inlet and outlet ports as said cylinder block rotates with respect to said valve means, pistons slidable in each of said cylinders including, an elongated rigid cylindrical piston element constructed in one piece and having at one end thereof a generally spherical projection, bearng means engaging said spherical projection, the other 2nd of said element defining a working face for the aiston, said cylindrical element serving to transfer the rydraulic force on said working face to said bearing means, an axial lubrication passage in said element exending from the working face through said spherical )rojection, an annular recess in said element extending .xially from the working face of the one piece element 0 a plane adjacent the projection thereby defining an ntegral cylindrical inner wall and an integral cylindrical uter wall, said recess dividing said working face into wo concentric end surface portions, the end surface portions of said walls lying in a generally radial plane and constituting a major portion of said working face, an annular plug fixed in said recess adjacent the working face, and a cam member for reciprocating said pistons and having a cam surface engaging said bearing means.

3. An axial piston hydraulic unit, comprising a cylinder block having a plurality of cylinders therein, a valve plate having inlet and outlet ports therein, each of said cylinders communicable successively with said inlet and outlet ports as the cylinder block rotates with respect to the valve plate; pistons slidable in each of said cylinders each including an elongated rigid cylindrical piston element constructed in one piece and having at one end thereof a generaly spherical projection adapted to be engaged by one of the slippers of the hydraulic device, the other end of said piston element defining a working face for the piston, said cylindrical element serving to transfer the hydraulic force On said working face to said bearing means, an axial lubrication passage in said element extending from the working face through said spherical projection, an annular recess in the cylindrical surface of said element extending from a plane adjacent the projection to a plane adjacent but spaced from said working face, said recess having an inner diameter substantially less than the diameter of the piston, said recess defining spaced cylindrical surfaces one adjacent each end thereof, and a separate cylindrical cover surrounding and enclosing said recess being thin with respect to said piston element, the ends of the cover engaging and fixed to the cylindrical surfaces on the one piece element, the outer diameter of the cover being equal to the desired piston diameter, at least one of said surfaces having a diameter throughout its length less than the inner diameter of the cover to permit inser-tion of the element in the cover; a slipper having a spherical socket therein engaging the spherical projection on each of said pistons, each of said slippers having a lubricating pocket opening into its associated spherical socket and adapted to receive lubricating fluid through the passage in the associated piston to lubricate the mating surfaces on the shperical projection and the spherical socket, a bear-ing surface on each of said slippers on the side of the slipper opposite said spherical socket, a second lubricating pocket in said bearing surface communicating with said first pocket whereby fluid may pass from the lubricating passage through the first pocket to the second pocket to lubricate said bearing surface, and a cam member for reciprocating said pistons having a camming surface engaging the bearing surfaces on said slippers.

4. An axial piston hydraulic unit, comprising: a cylinder block having a plurality of cylinders therein, a valve plate having inlet and outlet ports therein, each of said cylinders communicable successively with said inlet and outlet ports as the cylinder block rotates with respect to the valve plate, pistons slidable in each of said cylinders each including an elongated rigid cylindrical piston element constructed in one piece and having at one end thereof a generally spherical projection adapted to be engaged by one of the slippers of the hydraulic device, the other end of said piston element defining a working face for the piston, said cylindrical element serving to transfer the hydaulic force on said working face to said slippers, an axial lubrication passage in said element extending from the working face through said spherical projection, an annular recess extending axially from the working face of the one piece element to a plane adjacent the projection thereby defining an integral cylindrical inner wall and an integral cylindrical outer wall, said recess dividing said Working face into two concentric end surface portions, the end surface portions of said walls lying in a generally radial plane and constituting a major portion of said working face, and an annular plug fixed in said recess adjacent the working face; a slipper having a spherical socket therein engageing the spherical projection on each of said pistons, each of said slippers having a lubricating pocket opening into its associated spherical socket and adapted to receive lubricating fluid through the passage in the associated piston to lubricate the mating surfaces on the spherical projection and the spherical socket, a bearing surface on each of said slippers on the side of the slipper opposite said spherical socket, a second lubricating pocket in said bearing surface communicating with said first pocket whereby fluid may pass from the lubrication passage through the first pocket to the second pocket to lubricate said bearing surface, and a cam member for reciprocating said pistons having a camming surface engaging the bearing surfaces on said slippers.

References Cited by the Examiner UNITED STATES PATENTS 2,6943 83 11/ 1954 Larcen 92-260 2,880,042 3/1959 Budzich 103-l62 3,015,529 1/1962 Hard Castle 92-257 3,120,816 2/1964 Firth et al 103-174 V FOREIGN PATENTS 855,582 12/1960 Great Britain.

DONLEY I. STOCKING, Primary Examiner. MARK NEWMAN, Examiner. R. M. VARGO, W. L. FREEH, Assistant Examiners.

Po'loflo UNITED STATES PATENT OFFICE 569 CERTIFICATE OF CORRECTION Patent No. 3,319,575 Dated Mav 16, 19 7 Inventor(s) Arnold L. Havens It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

f" Column 1, line 4, cancel "Illinois" and insert "1 -Delaware-.

SIGNED AND SEALED MAR 01970 (SEAL) Attest:

Edward M. Fletcher, Ir. mm m WILLIAM E. 501 Attestmg Officer Commissioner of Patents 

1. A MULTIPLED PISTON HYDRAULIC TRANSLATING DEVICE, COMPRISING: A CYLINDER BLOCK HAVING A PLURALITY OF CYLINDERS THEREIN, VALVE MEANS HAVING INLET AND OUTLET PORTS, EACH OF SAID CYLINDERS COMMUNICABLE SERIALLY WITH SAID INLET AND OUTLET PORTS AS SAID CYLINDER BLOCK ROTATES WITH RESPECT TO SAID VALVE MEANS, PISTONS SLIDABLE IN EACH OF SAID CYLINDERS INCLUDING, AN ELONGATED RIGID CYLINDRICAL PISTON ELEMENT CONSTRUCTED IN ONE PIECE AND HAVING AT ONE END THEREOF A GENERALLY SPHERICAL PROJECTION, BEARING MEANS ENGAGING SAID SPHERICAL PROJECTION, THE OTHER END OF SAID ELEMENT DEFINING A WORKING FACE OF THE PISTON, SAID CYLINDRICAL ELEMENT SERVING TO TRANSFER THE HYDRAULIC FORCE ON SAID WORKING FACE TO SAID BEARING MEANS, AN AXIAL LUBRICATION PASSAGE IN SAID ELEMENT EXTENDING FROM THE WORKING FACE THROUGH SAID SPHERICAL PROJECTION, AN ANNULAR RECESS IN THE CYLINDRICAL SURFACE OF SAID ONE PIECE ELEMENT EXTENDING AXIALLY FROM A PLANE ADJACENT THE PROJECTION TO A PLANE ADJACENT BUT SPACED FROM SAID WORKING FACE, SAID RECESS HAVING AN INNER DIAMETER SUBSTANTIALLY LESS THAN THE DIAMETER OF THE PISTON, SAID RECESS DEFINING SPACED CYLINDRICAL SURFACES ON SAID ELEMENT ONE ADJACENT EACH END THEREOF, A SEPARATE CYLINDRICAL COVER SURROUNDING AND ENCLOSING SAID RECESS BEING THIN WITH RESPECT TO SAID PISTON ELEMENT, THE ENDS OF THE COVER ENGAGING AND FIXED TO THE CYLINDRICAL SURFACES ON THE ONE PIECE ELEMENT, THE OUTER DIAMETER OF THE COVER BEING EQUAL TO THE DESIRED PISTON DIAMETER, AT LEAST ONE OF SAID SURFACES HAVING A DIAMETER THROUGH ITS LENGTH LESS THAN THE INNER DIAMETER OF THE COVER TO PERMIT INSERTION OF THE ELEMENT IN THE COVER, AND A CAM MEMBER FOR RECIPROCATING SAID PISTONS AND HAVING A CAM SURFACE ENGAGING SAID BEARING MEANS. 